The company has loaded more than 40m records out of the 42m received so far from the UK's local councils and expects to complete loading for the entire electorate -- around 44.9m records -- by the end of this month.
Its view is more pessimistic than that of Skipton Information Group, which has said that the data it has collected so far points to an opt-out level of 28.5%.
Equifax said that while all Electoral Roll data is available for credit purposes, its use for general identity verification and direct marketing is being diminished.
Neil Munroe, external affairs director of Equifax, said: "When individuals opt out, companies have to find alternative sources in order to verify their identity, and this can slow down the process dramatically."
However, Equifax pointed out that this year's increase in opt-out is lower than the increase of five percentage points from 2003 to 2004. It said 13% of council returns showed a reduction in opt-out and a further 50% show increases in opt-out of less than 5%.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .